Process for preparing polydimethylsiloxanes on sulphonic acid cation exchange resins

ABSTRACT

The invention relates to a process for the targeted reorganization of polydimethylsiloxanes over sulphonic acid-containing cation exchange resins which have water contents of 8 to 25% by weight, and polydimethylsiloxanes thus prepared and the use thereof.

The invention relates to a process for the reorganization ofpolydimethylsiloxanes over sulphonic acid-containing cation exchangeresins which have water contents of 8 to 25% by weight, andpolydimethylsiloxanes thus prepared and the use thereof. Reorganizationis understood as meaning the rearrangement of the siloxane bonds inpolydimethylsiloxanes.

Low molecular weight polysiloxanes, in particular polydimethylsiloxanes,have become very important as cell-regulating stabilizers inpolyurethane foams, in particular polyurethane foams of the so-calledcold foam type (high resilience PU foams, HR polyurethane foams). Inprinciple, the typical cold foam stabilizers are polymers based onpolysiloxanes which are modified to greater or lesser extent by suitableorganic groups. In intrinsically stable systems, unmodifiedpolydimethylsiloxanes of the formula (I)

are preferably used, the total number of Si atoms may be N=n+2, where nmay be ≧1.

Industrially, these polydimethylsiloxanes are obtained by thereorganization/equilibration of siloxane cycles (such as, for example,D₃/D₄/D₅) or longer-chain polydimethylsiloxanes withhexamethyldisiloxane over acidic catalysts. Acidic catalysts used are,for example, acid-activated bleaching earths (bentonites,montmorillonites, Fuller's earths, etc.) and sulphonic acid-containing,macrocrosslinked cation exchange resins.

Thus, U.S. Pat. No. 3,694,405, which is hereby incorporated in itsentirety also with respect to the present invention, describes thereorganization/equilibration of organosiloxanes over macroreticular,sulphonic acid-containing cation exchange resins having a mean porevolume of at least 0.01 cm³/g. AMBERLYST 15 is used in Example 2 as atypical member of these catalysts. At a reaction temperature of 41° C.and residence times of 10 to 60 minutes, mixtures of siloxane cycles andhexamethyldisiloxane react over this acidic solid phase to giveequilibrates which have a relatively small proportion ofpolydimethylsiloxanes having chain lengths of N=3, 4, 5, 6 or 7, whichare present in each case only in proportions of 3 to 4% by weight, but ahigh proportion of high molecular weight oligomers (chain length N>7) of72.0 to 72.5% by weight. The catalysts used in U.S. Pat. No. 3,694,405have, according to the working examples, water contents of <1% byweight.

DE 103 01 355 (US 2004147703), which is hereby incorporated in itsentirety also with respect to the present invention, describes a processfor the preparation of equilibration products of organosiloxanes byrearrangement of the siloxane bond over a cation exchange resin, inwhich an organosiloxane used as starting material or an organosiloxanemixture is brought into contact at a temperature of 10° C. to 120° C.with a macrocrosslinked cation exchange resin containing sulphonic acidgroups and equilibrated organosiloxanes obtained are isolated, which ischaracterized in that a cation exchange resin whose product P ofspecific surface area and mean pore diameter is P≧2.2 10⁻³ m³/kg andwhose specific surface area A is ≧35 m²/g is used. A dried cationexchange resin or cation exchange resin having a water content of 5% byweight is used.

In relation to the equilibration of polydimethylsiloxanes over sulphonicacid-containing resins and the subsequent reactivation thereof bytreatment with low molecular weight siloxanes, EP 1 367 079 (US2003224925) refers to the importance of the water content of thesulphonic acid-containing cation exchange resin and indicates that awater load of <7, preferably 5, percent by mass should be established inorder to obtain optimum polymerization conditions.

The behaviour during use of polydimethylsiloxane compositions as HRpolyurethane foam stabilizers is very greatly dependent on the chainlength of the polydimethylsiloxanes present in the composition andrelative ratios thereof. Particularly suitable as HR polyurethane foamstabilizers are those polydimethylsiloxane compositions which have ahigh proportion of oligomers having a chain length N of 6 to 12 orpreferably consist exclusively of these. In order to separate suchparticularly suitable compositions of equilibrates, as can be obtained,for example, according to the teaching of U.S. Pat. No. 3,694,405,considerable separation effort is necessary.

DE-A-25 33 074 describes a process for the preparation of cold foamsusing, inter alia, polydimethylsiloxanes of the general formula (I),which is characterized in that polydimethylsiloxanes used are those inwhich N=(n+2)=4 to 12, the total content of polydimethylsiloxanes with Nequals 13 to 22 not being permitted to exceed 0.5% and it beingnecessary completely to separate off species with N>22. Here, referenceis made to the fact that it is very important to pay attention to thechain length distribution.

In EP 1 095 968, good foam stabilization power is confirmed for theproposed solution based on DE 25 33 074, but the poor dimensionstability is criticized. For eliminating this disadvantage, it isproposed to increase the proportions of polydimethylsiloxanes with Nfrom 7 to 9 to at least 90% by weight of the siloxane mixture. In orderto achieve this, distillation columns having a demanding design areused. By means of this time-consuming, energy-intensive and a henceexpensive preparation process, the desired products can be provided.

It was therefore an object of the present invention to provide a processfor the preparation of polysiloxanes, in particular polydimethylsiloxanecompositions, which are suitable as HR polyurethane foam stabilizers,which process avoids one or more of the disadvantages of the processesof the prior art. In particular, it was intended to provide a processfor the preparation of those suitable polydimethylsiloxanes which managewithout a complicated thermal separation step.

Surprisingly, it has now been found that polydimethylsiloxanes can beobtained in a composition directly suitable for use as HR polyurethanefoam stabilizers if the reorganization thereof is carried out over asulphonic acid-containing cation exchange resin which has a watercontent of 8 to 25% by weight.

The present invention also relates to polydimethylsiloxane compositionsobtainable by the process according to the invention, and the use of thecompositions as PU cold foam stabilizers.

The polydimethylsiloxane compositions obtainable by the processaccording to the invention surprisingly already have such small amountsof relatively high molecular weight fractions which may interfere duringthe foaming that it is possible to dispense with separating off thesubstances by a distillation.

The process according to the invention therefore has the advantage thata polydimethylsiloxane composition which can be used directly as astabilizer in polyurethane foams without it being necessary to carry outa complicated, expensive separation process is obtained directly by thereorganization. By means of the process according to the invention, inparticular a substantial increase in the selectivity with respect to thedesired products which can be used in the preparation of HR polyurethanefoams is achieved.

For the special case where any small amounts of relatively highmolecular weight polydimethylsiloxanes present or any low-boilingsiloxanes present in the composition obtained by the process accordingto the invention were to present problems in certain applications, thesecompounds can be removed from the composition by a simple distillation.

The polydimethylsiloxane compositions according to the invention, theuse thereof in PU-HR foam and the process for their preparation aredescribed below by way of example without it intended to limit theinvention to these being exemplary embodiments. When ranges, generalformulae or classes of compounds are stated below, these are notintended to comprise only the corresponding ranges or groups ofcompounds which are specifically mentioned but also all part-ranges andpart-groups of compounds which can be obtained by removal of individualvalues (ranges) or compounds. If documents are cited in the presentdescription, the content thereof is intended to belong completely to thedisclosure content of the present invention.

The process according to the invention for the preparation ofpolydimethylsiloxanes by reorganization of polydimethylsiloxanes oversulphonic acid-containing cation exchange resins is distinguished inthat cation exchange resins, in particular sulphonic acid-containingcation exchange resins, which have 8 to 25% by weight, preferably 10 to20% by weight, particularly preferably 12 to 18% by weight, of water areused. The water content can be determined on the basis of the method ofthe determination according to Karl Fischer, as described in DIN 51777,DGF E-III 10 and DGF C-III 13a.

The sulphonic acid-containing cation exchange resin used according tothe invention and having water contents in said ranges can be prepared,starting from cation exchange resins having higher water contents, byphysical and/or chemical drying. The physical drying can be effected,for example, in a drying oven, preferably at temperatures of 40 to 100°C., it being possible also to employ reduced pressure or to apply aninert gas stream for supporting the drying. Progress of the drying canbe observed and controlled by a regular water determination.Alternatively, the sulphonic acid-containing cation exchange resins usedaccording to the invention can also be chemically dried by bringing theminto contact with siloxanes of low molecular weight, as described, forexample, in EP 1 367 079.

The preparation of sulphonic acid-containing cation exchange resins usedaccording to the invention and having water contents of 8 to 25% byweight can optionally also start from cation exchange resins of reducedwater content. For this purpose, the cation exchange resin is broughtinto contact with water. In the simplest case, it is sufficient to storethe sulphonic acid-containing resin over a defined period in the usualatmosphere so that its intrinsic hygroscopicity leads to an increasedwater load.

If the sulphonic acid-containing cation exchange resin defined withrespect to its water content is used for the reorganization ofpolydimethylsiloxanes, it may be advantageous to add to the reactantsystem defined amounts of water, in particular to effectively counteractthe decrease in water content of the resin—in particular below the limitaccording to the invention of 8% by weight of water—caused byinteractions with other components of the reactant system. The meteringin can be effected continuously or batchwise. Any necessary addition ofwater can be determined by determination of the water present in thereaction discharge or alternatively by (regular) determination of thewater content in the cation exchange resin.

Cation exchange resins which may be used are in principle all sulphonicacid-containing cation exchange resins. Suitable cation exchange resinsare, for example, those which are prepared by sulphonation ofphenol/aldehyde condensates or of cooligomers of aromatic vinylcompounds. Examples of aromatic vinyl compounds for the preparation ofthe cooligomers are: styrene, vinyltoluene, vinylnaphthalene,vinylethylbenzene, methylstyrene, vinylchlorobenzene, vinylxylene anddivinylbenzene. In particular, the cooligomers which form by reaction ofstyrene with divinylbenzene are used as a precursor for the preparationof cation exchange resins having sulphonic acid groups. The resins canbe prepared in principle to be gel-like, macroporous or sponge-like. Theproperties of these resins, in particular specific surface area,porosity, stability, swelling or shrinkage and exchange capacity, can bevaried by the preparation process. Instead of gelatinous sulphonicacid-containing cation exchange resins, porous, preferably macroporous,sulphonic acid-containing cation exchange resins are preferably used.

In the process according to the invention, customary commerciallyavailable macroporous sulphonic acid-containing cation exchange resins,such as, for example, Purolite® C 145, Purolite® C 150 MBH, Lewatit® K2621, Lewatit® K 2629 or Lewatit® SP 121, can preferably be used intheir acidic, so-called “H form”. Among the suitable polymer phases ofthe styrene-divinylbenzene type which are commercially available, apreferred cation exchange resin here is one whose product P of specificsurface area and mean pore diameter is P≧2.2×10⁻³ m³/kg and whosespecific surface area A is ≧35 m²/g. A cation exchange resin whoseaverage specific surface area is in the range from 35 to 50 m²/g ispreferably used. Lewatit® K 2621 (Bayer AG) is particularly preferablyused as sulphonic acid-containing cation exchange resin.

In addition to the use of fresh cation exchange resin as catalyst, it ishowever also possible to use a sulphonic acid-containing resin alreadyused by the process according to the invention for the reorganization ofpolydimethylsiloxane compositions. Small residual amounts of reorganizedproduct which may then adhere to the surface of the catalyst usually donot present problems.

All customary straight-chain and/or cyclic siloxanes can be used assiloxane raw materials in the process according to the invention.Mixtures which comprise low molecular weight linear dimethylsiloxanestogether with cyclic siloxanes and hexamethyldisiloxane as a chainterminator are preferably reorganized. The upper limit of the viscosityof the polydimethylsiloxanes used here should preferably be not morethan 500 mPa·s. The chain length of the siloxanes used is preferably inthe range from 2 to 200 Si atoms.

Mixtures comprising or consisting of hexamethyldisiloxane and/oroctamethyltrisiloxane and siloxane cycles, such as, for example,hexamethylcyclotrisiloxane (D₃), octamethylcyclotetrasiloxane (D₄)and/or decamethylcyclopentasiloxane (D₅), can preferably be used assiloxane raw materials. Industrial mixtures containing or preferablyconsisting of hexamethyldisiloxane and D₄ and D₅ are preferably used.

The reorganization is preferably carried out at a temperature of 10° C.to 110° C., preferably at a temperature of 25° C. to 100° C. Thereorganization can optionally be carried out at reduced pressure,atmospheric pressure or superatmospheric pressure. Here, atmosphericpressure is to be understood as meaning, in addition to the definitionintroduced, the respective prevailing air pressure of the surroundingatmosphere. The reorganization is preferably carried out at a pressureof 950 mbar to 1100 mbar, particularly preferably at 1013 mbar.

It may be advantageous to carry out the reorganization in reaction timesof 20 minutes to 7 hours, preferably in 30 minutes to 5 hours. Bymaintaining said reaction times, high selectivity with respect topolydimethylsiloxanes having chain lengths of N=6 to N=12 in the rangeof 20 to 58% by mass can be achieved.

Very particularly preferably, the reorganization is carried out at atemperature of 25° C. to 100° C., a pressure of about 1013±10 mbar andin a period of 30 minutes to 5 hours.

If desired, the reorganization can also be carried out in the presenceof a solvent. Suitable solvents are all those solvents which are inertto cation exchange resin (catalyst) starting materials and productsduring the reorganization. However, the reorganization is particularlypreferably carried out in the absence of a solvent.

The amount of cation exchange resin to be used, based on the reactionmixture, is preferably from 1 to 15% by weight, particularly preferablyfrom 2 to 10% by weight, said cation exchange resin comprising waterwithin the abovementioned limits.

The process according to the invention can be carried out batchwise orcontinuously.

It may be advantageous to separate off a portion having a desiredboiling range from the reorganized product which is obtained as areaction mixture of the reorganization according to the invention. Theremaining residue of the reorganized product which does not have thedesired boiling range can be used again as starting material(organosiloxanes) in the reorganization. Particularly preferably, inparticular if the process is carried out continuously, a portion havinga desired boiling range is separated off from the polysiloxane mixtureobtained and the remainder which does not have the desired boiling rangeis used again as starting material (organosiloxanes) in thereorganization. This separation can be effected, for example, by asimple thermal separation (such as, for example, by simple distillationor by similar measures).

The reorganized products (dimethylsiloxane mixtures) obtained by theprocess according to the invention may contain, for example, low-boilingcompounds, such as, for example, hexamethyldisiloxane,octamethyltrisiloxane, decamethyltetrasiloxane anddodecamethylpentasiloxane (N₂, N₃, N₄ and N₅) or cyclic compounds, suchas D₄ and D₅, originating from the starting material composition. Thesecompounds (=sum (N₂−N₅+D₄+D₅)) are present in the reorganized productspreferably in proportions of 35 to 73% by mass. All these abovementionedlow molecular weight siloxane compounds can remain in the reorganizedproduct since as a rule they do not present problems for the subsequentfoaming process or have little effect. If desired, these compounds can,however, be completely or partly separated off from the reorganizedproduct. This separation, too, can be effected, for example, by a simplethermal separation (such as, for example, by stripping, the use of athin-film evaporator or by similar measures). The siloxane compoundsseparated off can then serve again as starting materials for furtherreorganization reactions according to the invention.

Such a separation of portions from the reorganized product obtainedaccording to the invention may be necessary in particular when parts ofthe reorganized product obtained prove to be troublesome for certainspecial applications.

For the use of dimethylsiloxane mixtures as a stabilizer in HRpolyurethane foams in the automotive sector, it may be advantageous, forexample from the point of view of avoiding fogging, to break off alllow-boiling siloxane compounds having a chain length of <N=6 by a simplethermal separation from the reorganized product obtained by the processaccording to the invention.

If desired for particular applications in HR polyurethane foam,relatively high-boiling polydimethylsiloxanes can also be thermallyseparated off from the reorganized products according to the inventionwhich can be used directly as a PU cold foam stabilizer. Theserelatively high-boiling polydimethylsiloxanes, too, can be recycled asstarting material into the reorganization according to the invention.

By means of the process according to the invention, thepolydimethylsiloxane compositions described below can be directlyprepared.

The compositions according to the invention containingpolydimethylsiloxanes of the formula (I)

having a chain length N=n+2, the sum of the proportions of thepolydimethylsiloxanes having the chain lengths N=6 and N=7 being ≧20% byweight, based on the total mass of the polydimethylsiloxanes, can beobtained by the above-described process according to the invention. Apreferred composition which has a proportion of polydimethylsiloxaneswith N=6 and N=7 of 20 to 35% by weight, based on the mass of thepolydimethylsiloxanes, can be obtained directly as a reorganizationproduct from the process according to the invention.

In the composition according to the invention, in particular thecomposition obtained directly as reorganized product, the proportion ofthe polydimethylsiloxanes of chain lengths N=6 to N=12 (N₆₋₁₂) ispreferably ≧20% by weight, preferably from 20 to 58% by weight, andparticularly preferably from 25 to 55% by weight, based on the mass ofthe polydimethylsiloxanes. The proportion of the polydimethylsiloxaneswith N≧13 (N_(≧13)) in the composition according to the invention, inparticular in the composition obtained directly as reorganized product,is preferably ≦7% by weight, preferably <6% by weight, particularlypreferably <5% by weight and particularly preferably from 0.2 to 3% byweight, based on the mass of the polydimethylsiloxanes.

In the composition according to the invention, the sum of the linearpolydimethylsiloxanes with N<6 (N₂ to N₅) and of the cyclic siloxaneshaving 4 or 5 silicon atoms (D₄+D₅) is preferably in the range of 35% byweight ≦Σ(N₂, N₃, N₄, N₅, D₄, D₅) 73% by weight, preferably in the rangeof 40% by weight ≦Σ(N₂, N₃, D₄, D₅)≦70% by weight, based on the totalmass of the polydimethylsiloxanes.

The compositions according to the invention, in particular thecompositions obtained directly as reorganized products, preferably have20 to 58% by weight of polydimethylsiloxanes having a chain length N of6 to 12 (N₆₋₁₂), <7% by weight of polydimethylsiloxanes having a chainlength N of ≧13 and 35 to 73% by weight of polysiloxanes having chainlengths of N=2 to 5 and cyclic siloxanes having 4 or 5 silicon atoms(N₂−N₅+D₄+D₅).

The compositions according to the invention, in particular thecompositions obtained directly as reorganized products, preferably have20 to 35% by weight of polydimethylsiloxanes having a chain length N of6 and 7, 3 to 23% by weight of polydimethylsiloxanes having a chainlength N of 8 to 12, ≦7% by weight of polydimethylsiloxanes having achain length N of 13 and 35 to 73% by weight of polydimethylsiloxaneshaving chain lengths of N=2 to 5 and cyclic siloxanes having 4 or 5silicon atoms.

The determination of the proportions of the polydimethylsiloxanes havingthe respective chain lengths can be effected, for example, by gaschromatography (GC) based on DIN 51 405. For example, the apparatus 5890series II from Hewlett-Packard with thermal conductivity detector (TCD)can be used as the gas chromatograph for the measurement. A suitableseparation column is, for example, a 1.8 m stainless steel column havingan internal diameter of 2 mm, filled with 10% of UCW 98 on Chromosorb WHP 80 to 100 mesh. Suitable chromatographic separation conditions are,for example: carrier gas: 30 ml/min of helium, injection blocktemperature: 300° C., detector temperature (TCD): 300° C., temperatureprogramme: 70 to 300° C. at 15° C./min, injection volume: 2 μl. Thequantitative determination of the components is effected by the standardaddition method. The standard chosen is D₄. The individual componentsare evaluated according to their signal area in relation to D₄ so that aresult in % by weight, calculated as D₄ equivalent, (% by weight) isobtained.

The mass ratio Q of the polydimethylsiloxanes having N equal to 6 or 7(sum N₆+N₇) to the polydimethylsiloxanes having N equal to 13 to 18 (sumN₁₃−N₁₈) in the composition according to the invention, in particularthe composition obtained directly as a reorganization product mixture,is preferably 4 to 60, preferably 10 to 55.

Particularly preferred compositions according to the invention containless than 1% by weight, of polydimethylsiloxanes of the formula (1) withN>18, preferably no polydimethylsiloxanes of the formula (1) with N>18.Such preferred compositions according to the invention can also beobtained, for example, by a simple distillation.

Another preferred composition according to the invention ofpolydimethylsiloxanes has a proportion of <5% by weight, preferably withzero proportion, of siloxane compounds, in particular linear and cyclicsiloxane compounds, having boiling points below the boiling point oftetradecamethylhexasiloxane (N=6) (245° C. at atmospheric pressure).Such preferred compositions according to the invention can be obtained,for example, by separating off the polydimethylsiloxanes having aboiling point below the boiling point of tetradecamethylhexasiloxane(N=6) (245° C. at atmospheric pressure) from the reorganization mixture,for example by simple distillation.

A particularly preferred composition according to the invention containsless than 1% by weight, of polydimethylsiloxanes of the formula (I) withN>18, preferably no polydimethylsiloxanes, and less than 1% by weight ofpolydimethylsiloxanes of chain lengths N≧13 and preferably a proportionof less than 1% by weight, preferably zero proportion, of siloxanecompounds Σ(N₂, N₃, N₄, N₅, D₄, D₅), which have a lower boiling pointthan tetradecamethylhexasiloxane (N=6). Such preferred compositions canbe obtained, starting from the reorganization product mixture, byremoving the corresponding compounds, for example by a simpledistillation.

The compositions according to the invention can be used as stabilizers,in particular cell-regulating stabilizers, in polyurethane foams,preferably polyurethane foams of the cold foam type. Compositionsaccording to the invention which are obtained directly as reorganizationproduct mixture are preferably used thereby.

As already described above, it is possible in particular according tothe invention for the compositions which are obtainable by the processaccording to the invention to be used as stabilizers in polyurethanefoams, preferably compositions used being those which are obtaineddirectly as process products from the reorganization, i.e. without afurther working-up step, in particular without a further separationstep.

The compositions according to the invention or the compositions obtainedaccording to the invention are particularly preferably used as astabilizer in (high resilience) polyurethane foams (also referred to ascold foams or HR foams), which are used in means of transport, inparticular in motor vehicles, such as, for example, cars, lorries orbuses. In the case of this use, it may be advantageous to use acomposition according to the invention which contains less than 1% byweight of compounds or preferably no compounds which have a boilingpoint which is lower than the boiling point of polydimethylsiloxanes ofthe formula (I) with N=6. By using these preferred compositions,emissions which are deposited in motor vehicles on the panes and maythus impair the vision can be avoided.

In the examples given below, the present invention is described by wayof example without it being intended to limit the invention, the rangeof application of which is evident from the entire description and theclaims, to the embodiments mentioned in the examples.

EXAMPLES

Determination of the proportions of the polydimethylsiloxanes having therespective chain lengths was carried out by gas chromatography (GC)based on DIN 51 405. A gas chromatograph of the type 5890 series II fromHewlett-Packard having a thermal conductivity detector (TCD) was usedfor the measurement. The separation column used was a 1.8 m stainlesssteel column having an internal diameter of 2 mm, filled with 10% of UCW98 on Chromosorb W HP 80 to 100 mesh. The chromatographic separationconditions set were the following: carrier gas: 30 ml/min of helium,injection block temperature: 300° C., detector temperature (TCD): 300°C., temperature programme: 70 to 300° C. at 15° C./min, injectionvolume: 2 μl. The quantitative determination of the components waseffected by the standard addition method. The standard chosen was D₄.The individual components were evaluated according to their signal areain relation to D₄ so that a result in % by weight, calculated as D₄equivalent, (% by weight), was obtained.

Examples 1 to 10 and Comparative Examples 1 and 2 Preparation of thePolysiloxanes

The examples were carried out partly as individual experiments (Examples8, 9 and 10) or as series of experiments (Examples 1 and 2, 3 and 4, 5to 7 and Comparative Experiments 1a and 1b).

In a 1 l four-necked flask equipped with a KPG stirrer, reflux condenserand internal thermometer, the respective siloxane reactants (for example228 g of hexamethyldisiloxane and 521 g of decamethylcyclopentasiloxane)were heated to the respective reaction temperature with stirring andthen treated with the predried cation exchange resin Lewatit® K 2621from Bayer AG (3% by mass, based on the total batch). Afterpredetermined times, samples were taken from the reaction mixture once(individual experiment) or several times (series of experiments) withthe aid of a syringe, upstream of which a syringe filter was connected,and said samples were transferred to a rolled-edge jar having a septumclosure, sealed and then analyzed by gas chromatography. The syringefilter served both for preserving the originally used amount of catalystin the reaction flask and for immediately stopping reorganization in thefreshly taken sample.

The following is stated in Table 1 below: the water content of thecation exchange resin acting as a catalyst, the reaction temperature,the reaction time and the results of the analysis of the end products:the proportion of siloxanes having a chain length N=6 and N=7, theproportion of siloxanes having the chain lengths N=13 to N=18 and theproportion of siloxanes D₄, D₅, N=2 and N=3.

TABLE 1 Results of Examples 1 to 10 and of Comparative Examples 1 and 2H₂O content Proportion of of the Proportion of Proportion of D4 + D5 +catalyst/% Reaction N6 + N7/% N13 − N18/% N2 + N3/% Examples by wt.Temp./° C. time/min by wt. by wt. by wt. 1 15 40 25 24.5 0.7 60 2 15 4045 28.3 2.0 43.1 3 12 30 30 25.3 0.7 60 4 12 30 50 29.2 2.0 45 5 20 3050 21.9 0.4 67 6 20 30 80 27.4 0.8 56 7 20 30 130 30 1.9 45 8 10 50 3030 3.1 33.2 9 10 50 20 21 2.7 63 10 20 50 40 25.4 5.4 29.3 Comp. 1a 5030 50 0.5 0 99 Comp. 1b 50 30 180 0.7 0 99 Comp. 2 5 40 180 16.7 11.724.2

As can be seen from Table 1, the reorganization compositions which wereobtained according to the invention have a substantially higherproportion of polydimethylsiloxanes with N=6+7 than those compositionswhich were obtained using sulphonic acid-containing cation exchangeresins which have a higher water content. As shown by ComparativeExample 2, in the case of a water content in the cation exchange resinwhich is too low, a composition which contains a high proportion ofpolydimethylsiloxanes with N=13 to 18 is obtained. By the use accordingto the invention of sulphonic acid-containing cation exchange resinshaving water contents of 8 to 25% by weight, preferably 10 to 20% byweight and particularly preferably 12 to 18% by weight, it is thuspossible directly to obtain compositions which, as will be shown in thefollowing examples, can be used directly as HR-RU stabilizers.

Examples 11 to 20 Distillative Purification of the ReorganizationProducts

In a 50 ml one-necked flask equipped with a magnetic stirring bar,Anschütz attachment and Claisen condenser, the respective siloxanemixtures were heated over an oil bath to an oil bath temperature of 215°C. with stirring. A pressure of 12 mbar or 1 mbar was applied thereby.The initially introduced mixture was cooled with ice water in order tocondense the distillate as completely as possible. The distillates andresidues obtained were analyzed as described above by gaschromatography. The results are listed in Table 2.

TABLE 2 Results of Examples 11 to 20 Proportion of Siloxane BottomProportion of Proportion of D4 + D5 + mixture product/ Pressure/ N6 +N7/% N13 − N18/% N2 + N3/% Example from Example distillate mbar by wt.by wt. by wt. 11 2 Distillate 12 26.9 1.9 45.6 12 2 Bottom 12 17.3 19.80.1 product 13 10 Distillate 12 27.6 0.1 41.4 14 10 Bottom 12 15.5 20.10.1 product 15 8 Distillate 12 31.2 0.1 43.6 16 8 Bottom 12 14.1 18.0 0product 17 9 Distillate 12 18.0 0 71.9 18 9 Bottom 12 18.2 20.3 0.1product 19 8 Distillate 1 49.9 0.1 9.7 20 10 Distillate 1 39.2 0.2 13.3

Examples 21 to 48 Preparation of the Flexible Polyurethane Cold FoamsFormulations Used: Formulation A:

90 parts of polyol having an OH number of 32 mg KOH/g and a molar massof 5500 g/mol, 10 parts of a polymer polyol (43% of SAN) having an OHnumber of 20 mg KOH/g and a molar mass of 5000 g/mol, 1.2 parts ofstabilizer consisting of a 10% strength solution of the correspondingsiloxane in a butanol-initiated polypropylene glycol having a molar massof 400, 4 parts of water, 0.9 part of diethanolamine, 0.4 part ofTEGOAMIN® MS 40 (Goldschmidt GmbH), 0.06 part of TEGOAMIN® BDE(Goldschmidt GmbH), 0.6 part of glycerol and 46 parts of isocyanate(T80=2,4- and 2,6-toluylene diisocyanate isomer mixture in the ratio80:20).

Formulation B:

73 parts of polyol having an OH number of 32 mg KOH/g and a molar massof 5500 g/mol, 27 parts of a polymer polyol (43% of SAN) having an OHnumber of 20 mg KOH/g and a molar mass of 5000 g/mol, 1.5 parts ofstabilizer consisting of a 10% strength solution of the correspondingsiloxane in a butanol-initiated polypropylene glycol having a molar massof 400, 4 parts of water, 0.9 part of diethanolamine, 0.4 part ofTEGOAMIN® 33 (Goldschmidt GmbH), 0.06 part of TEGOAMIN® BDE (GoldschmidtGmbH), 0.6 part of glycerol and 46 parts of isocyanate (T80=2,4- and2,6-toluylene diisocyanate isomer mixture in the ratio 80:20).

Formulation C:

70 parts of polyol (Voranol® HF 505 from Dow) having an OH number of 29mg KOH/g and a molar mass of about 6000 g/mol, 30 parts of a polymerpolyol (Voralux® HL 400) (43% of SAN) having an OH number of 33 mg KOH/gand a molar mass of 3000 g/mol, 0.8 part of stabilizer consisting of a10% strength solution of the corresponding siloxane in abutanol-initiated polypropylene glycol having a molar mass of 400, 4.5parts of water, 1.75 parts of diethanolamine, 0.12 part of TEGOAMIN® ZE1 (Goldschmidt GmbH), 0.08 part of TEGOAMIN® BDE (Goldschmidt GmbH),0.12 part of Kosmos® and 1.2 parts of Voranol® CP 1421 (from Dow) and 53parts of isocyanate (T80=2,4- and 2,6-toluylene diisocyanate isomermixture in the ratio 80:20).

Formulation D:

100 parts of polyol having an OH number of 35 mg KOH/g and a molar massof 5000 g/mol, 0.6 part of stabilizer in Examples 43 and 45 and 0.3 partin Examples 44, 46, 47 and 48, the stabilizer consisting of a 10%strength solution of the corresponding siloxane in a butanol-initiatedpolypropylene glycol having a molar mass of 400, 3 parts of water, 2parts of triethanolamine, 0.6 part of TEGOAMIN® 33 (Goldschmidt GmbH)and 0.2 part of diethanolamine and a mixture of 18.5 parts of polymericMDI (44V20 from Bayer) and 27.7 parts of TDI (T80).

Examples 21 to 25 Preparation of Moulded Foam Using Formulation A

The foams were prepared in a known manner by mixing all components,except for the isocyanate, in a beaker, then adding the isocyanate andstirring it in rapidly at a high stirrer speed. The reaction mixture wasthen introduced into an industrially used mould for an automobile seat,which mould was heated to a temperature of 65° C., and the material wasallowed to cure for 6 minutes. Thereafter, the compressibility (CO) ofthe foam was rated with values from 1 to 10, the value 1 representing avery open-cell foam and the value 10 a very closed-cell foam. Inaddition, the flow (FL) of the foaming material was rated with valuesfrom 1 to 5, 1 representing very good flow and 5 very poor flow. Theseeffects are displayed particularly at constrictions in the mould.Thereafter, the foams were cut open in order to assess the quality (skinand edge zone) and to determine the cell count (CC). In Table 3 below,the results of Examples 21 to 25 are summarized. The assessments and thesiloxane used in each case are mentioned. From the point of view of theevaluation of the performance characteristics, all HR-PU foams mentionedhere are good and technically usable.

TABLE 3 Results for Examples 21 to 25 using the formulation A EdgeSiloxane from Example CO FL CC Skin zone example 21 2 2 11 Good Good 422 2 2-3 11 Very Very 3 good good 23 1 1 10 Good Very 5 good 24 1 1 10Good Good 6 25 1-2 2 11 Good Good 7

Examples 26 to 33 Preparation of Slabstock Foam Using Formulation C

The foams were prepared in a known manner by mixing all components,except for the isocyanate, in a beaker, then adding the isocyanate andstirring it in rapidly at a high stirrer speed. Thereafter, the reactionmixture was introduced into a container lined with paper and having abase area of 28×28 cm. The height of rise (HR in cm) and the settling(SE in cm) were determined. The blow-off (BO) of the foam was rated withvalues from 0 to 3, 0 being allocated for poor or undetectable blow-offand 3 for very strong blow-off, values of 1 to 2 being desirable.Settling is designated as the decrease in the height of rise in cmwithin one minute after reaching the maximum height of rise. Blow-off isdesignated as the escape of the blowing gases from the opened cells ofthe foam.

After curing of the foam, it was cut open and the cell count (CC incm-1) was determined, and the quality of the foam (cell sizedistribution, edge zones) was generally assessed. In Table 4 below, theresults of Examples 26 to 33 are summarized. The assessments and thesiloxane used in each case are shown.

TABLE 4 Results for Examples 26 to 33 using formulation C Siloxane fromExample HR SE BO CC Quality Example 26 26.5 0.2 2 8 Good 12 27 26.8 0.61-2 9 Good 11 28 26.2 2.1 1 9 Good 15 (moderate) 29 27.8 0.2 1 7 Good 18(moderate) 30 25.9 1.7 1 8 Good 17 31 27.0 0.1 2 9 Good 14 32 26.3 1.9 18 Good 13 (moderate) 33 26.8 0.2 1 9 Good 10

Examples 34 to 48 Preparation of Moulded Foam Using Formulations B and D

The foams were prepared in a known manner by mixing all components,except for the isocyanate, in a beaker, then adding the isocyanate andstirring it in rapidly at a high stirrer speed. Thereafter, the reactionmixture was introduced into a cuboid mould having the dimensions40×40×10 cm which had been heated to a temperature of 40° C. in the caseof formulation D and to a temperature of 65° C. in the case offormulation B, and the material was allowed to cure for 6 minutes in thecase of formulation B and for 10 minutes in the case of formulation D.

Thereafter, the compression forces were measured. The foams werecompressed thereby 10 times to 50% of their height. Here, the 1stmeasured value (CO 1 in Newton) is a measure of the open-cell characterof the foam. Thereafter, complete (manual) compression (opening of thecompressible closed cells) was effected in order to be able to determinethe hardness of the compressed foam in the case of the 11th measuredvalue (CO 11 in Newton). Thereafter, the foams were cut open in order toassess skin and edge zone and to determine the cell count (CC). In Table5 below, the results of Examples 34 to 48 are summarized. Theassessments, the formulation (F) used and the siloxane used in each caseare shown.

TABLE 5 Results for Examples 34 to 48 using formulations B or D EdgeSiloxane from Example F CO 1 CO 11 CC Skin zone example 34 B 1754 185 11Good Good 9 35 B 1889 162 11 Good Good 10 36 B 1827 173 12 Good Good 237 B 1772 170 12 Good Good 2 38 B 1887 163 12 Good Good 5 39 B 1831 16612 Good Good 6 40 B 1784 165 12 Good Good 7 41 B 1550 155 12 Good Good19 42 B 1701 149 12 Good Good 20 43 D 1616 150 11 Good Good 1 44 D 1213132 10 Good Good 13 45 D 1002 111 11 Good Good 13 46 D 1405 132 10 GoodGood 3 47 D 1304 131 11 Good Good 19 48 D 1351 129 11 Good Good 20

It was possible to show that both the undistilled and the distilledreorganization compositions which were prepared by the process accordingto the invention are suitable as an additive (stabilizer, cellregulator) in HR-PU foam.

1. A process for rearranging siloxane bonds in a polydimethylsiloxanecomprising contacting a polydimethylsiloxane with a sulphonicacid-containing cation exchange resin having a water content of 8 to 25%by weight.
 2. The process according to claim 1, wherein thepolydimethylsiloxane is a mixture of hexamethyldisiloxane and/oroctamethyltrisiloxane and siloxane cycles.
 3. The process according toclaim 1, wherein the sulphonic acid-containing cation ion exchange resinincludes a cation exchange resin whose product P of specific surfacearea and mean pore diameter is P≧2.2×10³ m³/kg and whose specificsurface area A is ≧35 m²/g.
 4. The process according to claim 1, whereinthe sulphonic acid-containing cation ion exchange resin includes acation exchange resin whose average specific surface area is 35 to 50m²/g.
 5. The process according to claim 1, wherein the contacting iscarried out at a temperature of 10° C. to 110° C.
 6. The processaccording to claim 1, wherein the contacting is carried out for a periodof 30 minutes to 5 hours.
 7. The process according to claim 1, wherein aportion of the contacted polydimethylsiloxane having a desired boilingrange is separated off and a remainder portion of the contactedpolydimethylsiloxane which does not have the desired boiling range isused again as a starting material in said process.
 8. A compositioncontaining a polydimethylsiloxane of formula (1)

having a chain length N=n+2, wherein a proportion of thepolydimethylsiloxane with N=6 and N=7 being ≧20% by weight, based on themass of the polydimethylsiloxane.
 9. The composition according to claim8, wherein a proportion of the polydimethylsiloxane with N=6 to N=12 is20 to 58% by weight, based on the mass of the polydimethylsiloxane. 10.The composition according to claim 8, wherein a proportion of thepolydimethylsiloxane with N≧13 is <7% by weight, based on the mass ofthe polydimethylsiloxane.
 11. The composition according to claim 8,wherein the composition contains 20 to 58% by weight of apolydimethylsiloxane having a chain length N of 6 to 12, ≧7% by weightof a polydimethylsiloxane having a chain length N of ≧13 and 35 to 73%by weight of a polydimethylsiloxane having chain lengths of N=2 to 5 andcyclic siloxanes having 4 or 5 silicon atoms.
 12. The compositionaccording to claim 8, wherein the composition contains 20 to 35% byweight of a polydimethylsiloxane having a chain length N of 6 and 7, 3to 23% by weight of a polydimethylsiloxane having a chain length N of 8to 12, ≧7% by weight of a polydimethylsiloxane having a chain length Nof ≧13 and 35 to 73% by weight of a polydimethylsiloxane having chainlengths of N=2 to 5 and cyclic siloxanes having 4 or 5 silicon atoms.13. The composition according to claim 8, wherein a mass ratio Q of thepolydimethylsiloxane with N=6 or 7 to the polydimethylsiloxane with N=13to 18 is from 4 to
 60. 14. The composition according to claim 8, whereina sum of the proportions of the polydimethylsiloxane with N<6 and of theproportions of cyclic siloxanes having 4 or 5 silicon atoms is 40 to 70%by weight, based on the mass of the polydimethylsiloxane.
 15. Thecomposition according to claim 8, wherein the composition contains lessthan 1% of compounds which have a boiling point which is lower than theboiling point of a polydimethylsiloxane of the formula (1) with N=6. 16.A method of forming a polyurethane foam comprising adding a compositionin accordance to claim 8 to a reaction mixture including polyurethanefoam reactants. 17-18. (canceled)